Programs which depend on the special suspend-the-parent behavior of
vfork were always regarded as buggy...

So relying on the well-documented behavior of a system call is a bug? Did you even read about the scenario I described athttps://gnunet.org/vfork ? Before writing this, I looked around for existing information on vfork, but I didn't find anyone making a good argument (or even the claim) that relying on 'suspend-the-parent' was per-se buggy. (Naturally, the result would be non-portable for systems where fork==vfork, but then maybe implementing vfork as fork is the bug? ;-))